It’s not just those on the front lines of disaster or war who are at risk for post-traumatic stress disorder (PTSD), a new study finds. Emergency dispatchers who respond to 911 calls also suffer a mental toll, especially when taking distressing calls involving accidental death and suicide. The new study shows that 911 dispatchers’ indirect exposure to traumatic events can result in symptoms of PTSD.

“Usually research considers links between disorders and how much emotional distress is experienced on the scene of a traumatic event,” said study author Dr. Michelle Lilly of Northern Illinois University in a statement. “However, this is the first study on emergency dispatchers, who experience the trauma indirectly.”

For the study, published in the Journal of Traumatic Stress, researchers questioned 171 emergency dispatchers currently working in 24 U.S. states. The dispatchers — predominately white women around age 38 with more than 11 years of dispatching experience — were asked about the types of calls they answer and their corresponding emotional distress. They participants then rated the types of calls that caused great distress and were asked to recall the worst call they ever received.

About 16% of the calls dispatchers identified as their worst involved the unexpected injury or death of a child. About 13% were suicidal callers, 10% were police-officer shootings and another 10% involved the unexpected death of an adult.

The researchers report that the dispatchers experienced a high level of distress following 32% of potentially traumatic calls and that 3.5% of the dispatchers reported symptoms severe enough to be classified as PTSD.

Not knowing what happens after calls are dispatched is a significant stressor for dispatchers, ABC News reports. “We don’t know the end result. We don’t know if they made it. There is no formal communication back to us,” Monica Gavio, a coordinator for the Burlington County, New Jersey, 911 communications center, told ABC News.

“The results show the need to provide these workers with prevention and intervention support as is currently provided for their front-line colleagues. This includes briefings and training in ways to handle emotional distress,” study researcher and former 911 dispatcher Heather Pierce said in the statement.

In the study, researchers note the potential public safety concerns their findings bring to light:

Post-traumatic stress disorder symptoms that may be present in telecommunicators can impair decision-making abilities and functioning, which could pose signiﬁcant risk to the general population that relies on them to quickly and effectively coordinate an emergency response.

The researchers also suggest that their findings could contribute to the debate over the definition of a “traumatic event,” as official guidelines are set to be published next year.